Closing the gap: Follow-up observations of peculiar dusty objects close to Sgr A^* using ERIS

¹ I.Physikalisches Institut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
² Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
³ Astronomical Institute, Czech Academy of Sciences, Boční II 1401, 14100 Prague, Czech Republic
⁴ Indiana University, Department of Astronomy, Swain Hall West, 727 E 3 rd Street, Bloomington, IN 47405, USA
⁵ Charles University, Faculty of Mathematics and Physics, Astronomical Institute, V Holešovičkách 2, 18000 Prague, Czech Republic
⁶ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

^★ Corresponding author: peissker@ph1.uni-koeln.de

Received: 3 July 2025
Accepted: 1 October 2025

Abstract

Context. In addition to the supermassive black hole Sgr A*, the inner parsec of our Galactic center is home to numerous habitats that have yielded a cornucopia of scientific results. One of these environments is the S cluster, which consists of two distinct populations: the main-sequence S stars, and the dusty G objects. While the majority of the brightest S stars can be classified as young B stars, the G sources can be described as dusty objects whose nature is still under debate.

Aims. We focus on the most prominent G objects in the S cluster and follow their Keplerian trajectory around Sgr A*. With this, we test the predictions based on almost two decades of monitoring of the direct vicinity of our central supermassive black hole using NACO and SINFONI, formerly mounted at the Very Large Telescope (VLT). The goal is to increase the existing data baseline for G2/DSO, D9, and X7 to obtain insights into their evolution on their Keplerian trajectories. In addition, we revisit the massive young stellar object (YSO) X3 and determine the potential impact of its environment on this highly dynamic source.

Methods. The successor to the two instruments is called ERIS and offers upgraded optics and improved properties, including an enhanced spectral resolution. We used the IFU mode of ERIS, called SPIFFIER. We searched for the Doppler-shifted Brγ emission line to rediscover peculiar objects in the S cluster using SPIFFIER with the highest available spatial plate scale of 12.5 mas. Furthermore, we derived the Brγ luminosity of G2/DSO to inspect the degree of its change more than ten years after the pericenter passage. If present, a decrease in the Brγ luminosity of G2/DSO in the descending part of the orbit would directly affect the direction of the debate about its nature.

Results. All the sources we inspected were rediscovered in their predicted astrometric positions. This underlines the robustness of our monitoring efforts of the Galactic center. Furthermore, we found no signatures of a Brγ luminosity variability for G2/DSO. The enhanced capabilities offered by ERIS allowed us to recover the periodic pattern that resulted in the detection of D9, the first binary system in the S cluster. The bow-shock source X7 does not deviate from its proposed Keplerian orbit and follows its projected orbit toward the north. Finally, we verified prominent stellar outflows for the massive YSO X3.